/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.socket.client;

import java.net.URI;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.http.HttpHeaders;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.socket.WebSocketExtension;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.WebSocketHttpHeaders;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.util.UriComponentsBuilder;

/**
 * Abstract base class for {@link WebSocketClient} implementations.
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public abstract class AbstractWebSocketClient implements WebSocketClient {

    private static final Set<String> specialHeaders = new HashSet<>();

    /**
     * 静态方法添加头名称
     */
    static {
        specialHeaders.add("cache-control");
        specialHeaders.add("connection");
        specialHeaders.add("host");
        specialHeaders.add("sec-websocket-extensions");
        specialHeaders.add("sec-websocket-key");
        specialHeaders.add("sec-websocket-protocol");
        specialHeaders.add("sec-websocket-version");
        specialHeaders.add("pragma");
        specialHeaders.add("upgrade");
    }


    protected final Log logger = LogFactory.getLog(getClass());


    /**
     * 握手
     * @param webSocketHandler
     * @param uriTemplate
     * @param uriVars
     * @return
     */
    @Override
    public ListenableFuture<WebSocketSession> doHandshake(WebSocketHandler webSocketHandler,
                                                          String uriTemplate, Object... uriVars) {

        Assert.notNull(uriTemplate, "'uriTemplate' must not be null");
        URI uri = UriComponentsBuilder.fromUriString(uriTemplate).buildAndExpand(uriVars).encode().toUri();
        return doHandshake(webSocketHandler, null, uri);
    }

    @Override
    public final ListenableFuture<WebSocketSession> doHandshake(WebSocketHandler webSocketHandler,
                                                                @Nullable WebSocketHttpHeaders headers, URI uri) {

        Assert.notNull(webSocketHandler, "WebSocketHandler must not be null");
        assertUri(uri);

        if (logger.isDebugEnabled()) {
            logger.debug("Connecting to " + uri);
        }
        // http 请求头
        HttpHeaders headersToUse = new HttpHeaders();
        if (headers != null) {
            // 循环设置请求头信息
            headers.forEach((header, values) -> {
                if (values != null && !specialHeaders.contains(header.toLowerCase())) {
                    headersToUse.put(header, values);
                }
            });
        }

        // webSocket 协议中的 subProtocols
        List<String> subProtocols =
                (headers != null ? headers.getSecWebSocketProtocol() : Collections.emptyList());
        // 拓展列表
        List<WebSocketExtension> extensions =
                (headers != null ? headers.getSecWebSocketExtensions() : Collections.emptyList());

        // 握手
        return doHandshakeInternal(webSocketHandler, headersToUse, uri, subProtocols, extensions,
                Collections.emptyMap());
    }

    protected void assertUri(URI uri) {
        Assert.notNull(uri, "URI must not be null");
        String scheme = uri.getScheme();
        // 类型判断 属于ws 还是wss
        if (!"ws".equals(scheme) && !"wss".equals(scheme)) {
            throw new IllegalArgumentException("Invalid scheme: " + scheme);
        }
    }

    /**
     * Perform the actual handshake to establish a connection to the server.
     *
     * @param webSocketHandler the client-side handler for WebSocket messages
     * @param headers          the HTTP headers to use for the handshake, with unwanted (forbidden)
     *                         headers filtered out (never {@code null})
     * @param uri              the target URI for the handshake (never {@code null})
     * @param subProtocols     requested sub-protocols, or an empty list
     * @param extensions       requested WebSocket extensions, or an empty list
     * @param attributes       attributes to associate with the WebSocketSession, i.e. via
     *                         {@link WebSocketSession#getAttributes()}; currently always an empty map.
     * @return the established WebSocket session wrapped in a ListenableFuture.
     */
    protected abstract ListenableFuture<WebSocketSession> doHandshakeInternal(WebSocketHandler webSocketHandler,
                                                                              HttpHeaders headers, URI uri, List<String> subProtocols, List<WebSocketExtension> extensions,
                                                                              Map<String, Object> attributes);

}
